This invention relates generally to methods and apparatus for operating a switching facility of the type having several switching panels in an electric power distribution network, and more particularly, to a system wherein there is provided protection against switching errors by observing predetermined safety conditions. Such error protection is achieved by interlocking respective switches such that switching is prevented until all safety conditions pertaining to the switching operation are met. Such safety conditions include, for example, disconnect switches must not be switched under load; grounding switches must be switched only after the system conductor which is to be grounded is free of voltage; and circuit breakers must not be closed if a disconnect switch in the same circuit is in a "trouble" position.
In accordance with the journal "Siemens-Energietechnik", 1981, no. 1, pages 20-23, it is known in the field of electric switching error-protection equipment to achieve interlocking of switches by means of contacts of auxiliary relays which are operated independently of the positions of the switches. The relay contacts are wired between the individual equipment associated with a switch panel in a so-called interlocking cable harness, and equipments of different switch panels by means of cross wiring. In known arrangements, the cross wiring, in particular, is relatively elaborate and any expansion requires additional wiring for all existing equipments. The requirements of additional wiring also applies to expansions which are purely internal to the switch panel. Accordingly, with such an electromechanical design for an interlocking system there is the additional danger that defects or discontinuities in the wiring remain undetected.
It is, therefore, an object of this invention to provide a method of operating a multipanel switch for an electric power distribution network which does not require relays, interlock cable harnesses, or cross wiring, to perform the interlocking function.